1. Field of the Invention
The present invention relates to a press-forming die for glass elements. In particular, the present invention relates to a die for press-forming glass elements, which makes it possible to form and process glass elements for an optical IC with excellent die release performance.
2. Description of the Related Art
A method for press-forming glass elements by means of a press-forming process has been hitherto used. In general, such a method raises several issues including, for example, the die release performance between the glass element and the forming die after the forming process, the surface roughness of the glass element, and the surface quality such as whether or not any scratch exists. Various countermeasures have been investigated, including, for example, the forming condition and the selection of the material for the forming die.
Highly accurate forming operation is required especially when an optical lens is produced. Further, the material for the die raises several issues including the deterioration of die release performance resulting from the reactivity with glass during the forming process at a high temperature, and the surface scratch on the glass-pressing surface. As a solution for such issues, the following technique has been disclosed. That is, in order to make the surface roughness of the formed optical lens to be several hundredth xcexcm, a die is used, in which a cemented carbide is used as a base material, and a noble metal thin film, which contains a major component of iridium, is formed in a degree of several xcexcm on the surface of the cemented carbide (see Japanese Laid-Open Patent Publication No. 61-256931). According to this technique, the forming condition of this method is such that lead oxide glass is used as a lens material, the heating temperature is 630xc2x0 C., the press operation is performed for 2 minutes at a press pressure of 40 kg/cm2, and the open process temperature after cooling is 380xc2x0 C.
On the other hand, for example, when a glass element for optical IC is press-formed and processed, the excellent die release performance is an important factor as well in the same manner as in the forming process for the optical lens. However, the highly accurate operation is not necessarily required concerning the surface scratch, i.e., the processing accuracy of the die. Usually, when the die is subjected to grinding processing by using a diamond grinding wheel, it is inevitable (in view of the processing technique) that the surface roughness of about 0.5 xcexcm remains at most. However, the surface roughness of this degree is within the allowable range when the product is used for the glass element for optical IC.
When the glass element for optical IC is press-formed and processed, the type of the glass material is selected and used depending on the use or application of the glass element for optical IC. The forming condition is different from those used for processing the optical lens as described above. In general, the forming operation for the glass element for optical IC is performed at a high temperature and at a high pressure, in which the press time is short. Further, the glass element for optical IC is used such that V-shaped grooves are formed on the glass substrate by means of the forming operation, and a glass fiber is positioned and arranged in the grooves. In such a case, the glass fiber is fixed by using an adhesive. It is also necessary to consider the adhesive performance during such a process.
The present invention has been made taking such problems into consideration, an object of which is to provide a die for press-forming glass elements, to be used to produce the glass elements by means of the press-forming process by using a variety of glass materials appropriately selected depending on the use or application of the glass elements, in which an appropriate degree of surface roughness of the glass element is ensured, the die release performance is excellent, and the adhesive performance for an adhesive is also excellent when a glass fiber is arranged in V-shaped grooves formed on a glass substrate.
According to the present invention, there is provided a die for press-forming glass elements, comprising at least a platinum thin film having a thickness of 0.01 to 5 xcexcm formed on an outermost surface of a press face of a cemented carbide base material.
Those usable as the cemented carbide base material include those containing a major component of tungsten carbide. However, there is no limitation thereto.
As for the thickness of the platinum thin film, a thin layer is sufficiently used provided that the thin film on the die surface is not peeled off due to repeated use. The preferred thickness is determined according to such a viewpoint. The thickness is determined in the same manner for the other aspects of the invention described later on. In the present invention, it is also possible to preferably use the die in which a nickel thin film having a thickness of 0.05 to 0.5 xcexcm is allowed to intervene between the cemented carbide base material and the platinum thin film.
In a preferred embodiment, it is also possible that an alloy thin film having a thickness of 0.01 to 5 xcexcm, which contains 10 to 70% by weight of iridium and 30 to 90% by weight of one or more species of metals selected from metals of the platinum group except for iridium, is allowed to intervene between the cemented carbide base material and the platinum thin film. In this embodiment, it is more preferable that the species of metal of the platinum group except for iridium is only platinum.
The die constructed as described above makes it possible to perform the press-forming operation in which the die release performance is excellent without any adhesion or deposition of softened glass material onto the die, even in the case of the use of any one of various glass materials selected depending on the use or application of the glass element, including, for example, crystalline glass materials (non-crystalline materials), chemically tempered glass materials (materials before the ion exchange treatment), and borosilicate glass. Further, V-shaped grooves are formed on the glass substrate as the material for the glass element, and an optical fiber is arranged in the grooves by using an adhesive. Therefore, the adhesive performance is excellent for the optical fiber to be glued to the glass substrate.
It is preferable that the glass element subjected to the press-forming has a surface roughness (Rmax) within a range of 0.4 to 1.2 xcexcm.
In the present invention, the glass element for optical IC, which belongs to the glass element, is not necessarily subjected to precision machining into one having an extremely small degree of surface roughness. Especially, for example, when the predetermined grooves for embedding the optical fiber are provided by means of the press-forming on a connector part for optically coupling the optical fiber and the IC chip, it is sufficient to give a processing accuracy in such a degree that the optical fiber can be positioned at a submicron level.
An allowable value in view of the positioning accuracy for the optical fiber (single mode), i.e., an upper limit value of the surface roughness of the glass element is preferably not more than 1.2 xcexcm as represented by Rmax, more desirably not more than 1.0 xcexcm. On the other hand, from a viewpoint to improve the adhesive performance for the glass fiber to be glued to the glass substrate, it is preferable to increase the adhesion area by providing a certain degree of surface roughness. A lower limit value of the surface roughness of the glass element is preferably not less than 0.4 xcexcm as represented by Rmax, more desirably not less than 0.5 xcexcm.
The range of the surface roughness is especially preferred when the glass surface is metallized to fix and secure the optical fiber by means of soldering. The surface roughness of the glass element is herein used as an evaluation standard. However, the surface roughness of the glass element is equivalent to the roughness of the forming surface of the die in the case of the glass press-forming process in which transfer is effected in a well suited manner.
The press-forming die according to the present invention is excellent in die release performance. The die is also excellent in adhesive performance for the optical fiber adhered to the glass substrate by the aid of an adhesive, and the die is sufficient to ensure the processing accuracy as described above. The press-forming die according to the present invention is more preferably used for such use or application.
When the glass element is press-formed by using the press-forming die according to the present invention, a difference in die release performance remarkably appears by using a glass material having a softening point of not less than 600xc2x0 C.
The softening point of the glass material differs as follows. That is, for example, the softening point of a crystalline glass material (produced by NGK Insulators, Ltd., trade name: Miracron PP-4) is about 550xc2x0 C. The softening point of an optical glass material (produced by NGK Insulators, Ltd., trade name: Miracron PC-4) is about 580xc2x0 C. The softening point of a borosilicate optical glass (BK-7) is about 620xc2x0 C. The softening point of a borosilicate glass (produced by Corning, trade name: Pyrex) is about 820xc2x0 C. Therefore, when the glass element is formed, the forming condition such as the forming temperature is changed depending on the final use or application. However, even when the forming condition is adjusted as described above, if a glass material having a high softening point is used, the forming temperature is of course high (usually, the forming temperature is about xe2x80x9csoftening point +10 to 50xc2x0 C.xe2x80x9d). For this reason, a tendency is observed, in which the die release performance is deteriorated resulting from the reactivity between the forming die and the glass material and the surface oxidation of the forming die. This tendency is conspicuous when the softening point of the glass material exceeds 600xc2x0 C.
The use of the forming die according to the present invention provides the forming technique in which the die release performance is extremely excellent regardless of the type of the glass material, especially when a glass material having a high softening point is used. The phenomenon of the surface oxidation of the forming die is conspicuous in the case of the conventional material such as a Ptxe2x80x94Ir alloy. Even when the forming operation is performed in a nitrogen gas atmosphere as a means to avoid the oxidation, it is difficult to completely dissolve the drawback, because the nitrogen gas itself to be used contains oxygen gas in a degree of 10 ppm. On the contrary, the use of the press-forming die according to the present invention, in which the Pt thin film that is relatively difficult to be oxidized is formed on the outermost surface of the press face, makes it possible to preferably perform the press-forming operation even in the nitrogen gas atmosphere.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.